Production of meeamine from lime



' ;,1.3,5-triazine. some of its reactions-suggestthat Patented Mar. 20, 1951 I aA 'I ES OFFICE ERRODUGTION 10F MEEAMINEr FRGMKLIME :NITRGGEN jJijhnst'o'ne iSJMabkay, OI'd'QGreenWih Conm,' as- ""s'ignor' to American (lyanamidflompany, New

"'Yo'i'kjN. Y., a eorporation'pf" Maine NorDrawing. .--*Application:MaA,.1948,

SeriaLrNo.l. 25;0-7

1 Claims. (Cl5260"249i'7) "Th inv ll ates to lithe :pre'p of 11A istill "further fiobject toi "this invention "is to imlamine. .lprepare vmelamine tdirectlyufrom; calcium cyan- TThec mpounds-commonly" known :as'imeiamine gamide .an'cLAin, articular, i'from Y lime lnitrogen -'i'sfa white crystallineysolidlhaving.elmelting point id CEMumwmnarhideL w t t use! of about 354"C. It""has"'the' empiricarform'ula arating gyanami de or dicyafiaiamide -C3N6HG and is generally believed tohaive the has been fo und that rnel a rnine,can be pro 1T611Wing fstlucturalirformulal ::duced :by reacting .e'alcium icyanamide, :ea'rbon /pz -rdioxide ammonia and watersin .an autoclave at temperatures rangingfrOmabOut-ZOO .Ctto about Z? lf =-400"=,C.-u-nciler the autogenously producedpres- -sure=forafrom-about leto about-H 16: hours.

-C .;monium-. earbonate and bicarbonate are equiv- 1 salents don combinations. of'= earbon'::dioxide, iammonia, and water, as explained below. .1.'I'l1e=;'preecise :chemicaleequations .-:invo1vedvare:1as.,yet ob- ;scureaandsapplicant idoes not Wish to -be'-:bound sbyrany-z'supposedzcourse-ofirea'etion. lt sufiices to ssay *zthat whenrcalcium scyanamide, sammonia,

As "such, it is "frequently call-ed 2 ,'4-,'6'triaminol5 it"may:also existlinwholeprnn' part-in one or .IIIIOIB isomericforms-* such as 2o carbonadioxidaiandv waterrare rea'cted .undercthe 1 zispecified: conditions'amelamine is "obtained in fair HNLfC Q=NH wield.

Asfihe purerziormszd ealcium cyanamide are f K .QNQH --=expen"sive,i the:applicant prefers =to use the "rela Y v tively i-i'mpure' but 'Cheap form Lkno'w-n in :ebm- Qty 4 amerce as limemitrogen. i Li-me nitrogen commonly and analyzes from "*60 65'% 'calc'ium '-'cyanamide, the

remainder 1 being limep 'grazihitegand other imf purities. The' -lime nitrogen-used" iii-the examples described below contained about 43% calcium.

- -6' \(hNH Although the 'reaetiofitakes place within the N *range -cif 200 400"- C.,it is prferable to conduct h theprocess within' the more limited range of '300-4'00 C.,'-andit is--even' more desirable-tense NH; a1 temperature of about"-350 C. *Thetable, which Absolute proof of the exact structure of mela- W W effect of temperature'onvyleld mine, "or'its*supp'osed'isomers,"has'notbeen def-- initely established, but the-term melamine is Table commonlyzrecegnizedtandiis usedi herein as in- .lsfofi its production have utilized lcyanamide-or di- Efij' theautogenously developed'pres :nyandiamide as starting materials. IIheSeLlatter Y compounds yield melamine" infair to good yields by p01ymerization uponaheating,either alone or,- kReammimmitions {melamine withrseveral different-typesand kinds of\ solvents, v -:diluents,rcatalystsfletc. i-:A ew=:other1organic nih g a .Perwcem; trogen compounds. for example, guanidine salts, mime Temper iPmsureyji yiGmm have been salcl to yield small percentages of mela- Hrs. ture, 0. p. s, i. f, in lime mine along with various other compounds when nitrogen heated at temperatures up to about 200 C.

An object of this invention is to prepare melanogl cg ed I 1% mine from inexpensive raw materials. I 2 350 3:100 435 A further ob ect is to prepare melamine 1n a 2 400 800 27 one step process.

amples.

Increasing the time of reaction increases the yield slightly. In one experiment 100 g. of lime nitrogen (1.09 moles) and 90 g. of ammonium bicarbonate (1.15 moles) were reacted for two hours at 350 C., yielding 14.7 g. of melamine.

or 42.2%. When an identical run was held 16.

hours at 350 C., the yield was 16.1 g., or 47.2%.

Melamine can be obtained by the process of this application using various proportions of reactants. However, the best yields are obtained when the ammonia, carbon dioxide, and water are present in about the same proportions as they are present in ammonium bicarbonate, that is,

1:1: 1, and the mole ratio of carbon dioxide to the total calcium in the lime nitrogen is about 0.95:1.

as ammonium carbonate. When an excess of ammonia is introduced, it reacts with ammonium bicarbonate to yield ammonium carbonate.

In the preceding examples, melamine was recovered from" the reaction mass, removed from many of these methods to the removal of melamine formed by the present process. One such -me'thod comprises blowing the reaction mass from The yield of melamine decreases with decreasing lime nitrogenzammonium bicarbonate ratio.

For example, 40 parts by weight of the lime nitrogen were reacted with 32 partsof ammonium bicarbonate in a 300 cc. autoclave for two hours g at 350 C. under the autogen'ously developed pressure, with a melamine yield of 43.5%, and when 100 parts of lime nitrogen were reacted with 90 parts of ammonium bicarbonate underidentical conditions, the yield of melamine fell to 32.2%.

A 50:90 ratio under the same conditions gave only a negligible yield of melamine. I Increasing the proportion of the ammonia or the carbon dioxide over that'available in ammonium bicarbonate does not increase the yield of melamine, as shown in the two following ex- One hundred grams of lime nitrogen, 50 grams of ammonium bicarbonate, and grams of ammonia (an equivalent of 0.63 mole of ammonium carbonate and 0.55 mole of excess ammonia) were reacted in a 300 cc. autoclave for two hours at 350C. under a pressure of 3900 lbs/sq. in. The yield of melamine was 8.7 grams, a yield of 25.5% based on the nitrogen in the lime nitrogen.

One hundred grams of lime nitrogen (1.09 moles), 90 grams of ammonium bicarbonate (1.15 moles), and 35 grams of carbon dioxide were reacted for two hours at 350 C. in a 300 cc.

autoclave under a pressure of 1475 lbs/sq. in., resulting in 11.5 grams of melamine, a yield of 33.6%.

The process is operable over a wide pressure range. Melamine can be obtained at pressures as low as about 500 lbs/sq. in., and also at pressures of the order of 5000 lbs/sq. in., and even higher.

In the foregoing examples, the use of ammonium bicarbonate has been described instead of mixtures of its components. It willbe readily ob served by those skilled in the art that it is not necessary to use ammonium bicarbonate as a source of ammonia, carbon dioxide, and water, but that it is simply a convenient means of introducing the three named reactants into the autoclave. It will be obvious that ammonia, carbon dioxide, and water may be introduced into the autoclave either as such or combined in the form of ammonium bicarbonate. Mixtures of these three reactants and ammonium bicarbonate are also suitable. Consequently, when ammonia, carbon dioxide, and water are referred to in this specification, it is to be understood that they may be present assuch, as ammonium bicarbonate, or

the autoclave, leaching the mass with a suitable solvent such as hot water, and crystallizing the melamine from the solvent.

.W-hilethe process ofthe. presentinvention has been described with reference to specific embodiments, it is not to be considered as limited thereto buts'hould be construed solely in" accordance with the scope of the appended'claims.

I I claim: .1

1. The method .01: makingmelamine which comprises reacting calcium cyanamide, ammonia, carbon dioxide and water in a closed reaction zone at a temperature/within the range of 200-400 C. and at a pressure of at least 500 p. s. i., the weight ratio of calcium cyanamide to ammonium bicarbonate stoichiometrically equivalent to said ammonia, carbon dioxide and water being in excess of 50 2 90, and recovering the thus-formed melamine.

2. The method according to claim 1 in which L calcium cyanamide is present as lime nitrogen.

3. The method of making melamine which comprises reacting about 40 parts by weight of lime nitrogen with about igparts of ammonium bicarbonate in a closed reaction zone at a temperature within the range of 200 C. to 400 C. at a pressure of at least 500 lbs/sq. in. under melamine-forming conditions, and recovering the thus-formed melamine.

4. The method of making melamine .which comprises reacting together about 1 mole of'calcium cyanamide, about 1 mole of ammonia, about 1 mole of carbon dioxide, and about 1 mole of water in a closed reaction zone at a temperature of about 350 C. and a pressure of at least 500 lbs/sq. in.

J OHNSTONE S. MACKAY.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,380,223 Lidholm May 31, 1921 2,114,280 Aldred Apr. 19, 1938 2,164,705 Fisch July 4, 1939 2,191,361 Widmer Feb. 20, 1 940 2,286,349 Davis June 16, 1942 FOREIGN PATENTS Number Country Date Great Britain Dec. 19, 1946 

1. THE METHOD OF MAKING MELAMINE WHICH COMPRISES REACTING CALCIUM CYANAMIDE, AMMONIA, CARBON DIOXIDE AND WATER IN A CLOSED REACTION ZONE AT A TEMPERATURE WITHIN THE RANGE OF 200-400* C. AND AT A PRESSURE OF AT LEAST 500 P.S.I., THE WEIGHT RATIO OF CALCIUM CYANAMIDE TO AMMONIUM BICARBONATE STOICHIOMETRICALLY EQUIVALENT TO SAID AMMONIA, CARBON DIOXIDE AND WATER BEING IN EXCESS OF 50:90, AND RECOVERING THE THUS-FORMED MELAMINE. 